There are a number of microfabrication technologies that have been utilized for making microstructures (e.g., micromechanical devices, microelectromechanical devices) by what may be characterized as micromachining, including LIGA (Lithographie, Galvonoformung, Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surface micromachining, micro electrodischarge machining (EDM), laser micromachining, 3-D stereolithography, and other techniques. Bulk micromachining has been utilized for making relatively simple micromechanical structures. Bulk micromachining generally entails cutting or machining a bulk substrate using an appropriate etchant (e.g., using liquid crystal-plane selective etchants; using deep reactive ion etching techniques). Another micromachining technique that allows for the formation of significantly more complex microstructures is surface micromachining. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material using an appropriate substrate which functions as the foundation for the resulting microstructure. Various patterning operations (collectively including masking, etching, and mask removal operations) may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructure(s). After the microstructure(s) has been defined in this general manner, the various sacrificial layers are removed by exposing the microstructure(s) and the various sacrificial layers to one or more etchants. This is commonly called “releasing” the microstructure(s) from the substrate, typically to allow at least some degree of relative movement between the microstructure(s) and the substrate. The etchant is biased to the sacrificial material to remove the same at a greater rate than the structural material. Preferably, the microstructure(s) is released without allowing the etchant to have an adverse impact on the structural material of the microstructure(s).
Microelectromechanical systems are typically actuated in a manner where the direction of the load forces are substantially collinear with the motion of the actuator. However, for some actuation systems, the load may be permitted to move in a path that is not collinear with the motion of the actuator (e.g., where the load moves out of plane). Off-axis forces (i.e., non-collinear) can result that can be detrimental to the operation of the actuator. For instance, actuator electrodes may short together or portions of the actuator may contact other surfaces of the microelectromechanical system, thereby adversely impacting the motion of the actuator. It would be desirable for the portion the load force that is transmitted to the actuator to be constrained to be at least substantially collinear with the motion of the actuator, thereby facilitating the proper operation of the actuator. In other words, it would be desirable for off-axis components of the load force to be isolated from the actuator by a force isolation system of sorts, or equivalently, by some way of constraining the direction of the force acting on the actuator. For most applications, and particularly for applications involving precise positioning of optical elements, it would be further desirable to provide this force isolation function in a manner that does not exhibit hysteretic behavior. This generally means that it would be desirable for none of the surfaces of such a force isolation system to come into contact or rub during normal operation of the microelectromechanical system.